Manufacture of detonating fuse cord

ABSTRACT

A method of manufacturing a detonating cord having a dual explosive core is described. The total quantity of explosive in the dual core varies along the length of the cord and the product is useful in metal expansion operations.

Unite States atent elsli 51 Oct. 17,1972

[ MANUFACTURE OF DETONATING FUSE CORD David Martin Welsh, Brownsburg,Quebec, Canada Inventor:

[73] Assignee: Canadian Safety Fuse Company Limited, Montreal, Quebec,Canada Filed: Jan. 19, 1970 Appl. No.: 3,859

[30] Foreign Application Priority Data Nov. 10, 1969 Canada ..067,l50

US. Cl. ..86/l R, 102/27 R Int. Cl. ..C06b 21/02 Field of Search 102/27;86/1; 264/3 References Cited UNITED STATES PATENTS 2,008,046 7/1935Snelling 102/27 R 2,877,708 3/1959 Rey ..102/27 2,784,638 3/1957 Dielset a1 ..264/3 3,368,485 2/1968 Klotz ..102/27 2,939,176 6/1960 Adelman..264/3 3,160,949 12/1964 Bussey et a1. ..l02/23 X 3,320,883 5/1967Welsh ..102/27 3,407,731 10/1968 Evans ..l02/27 Primary Examiner-SamuelW. Engle Attorney-Bernard F. Roussin 1 1 ABSTRACT A method ofmanufacturing a detonating cord having a dual explosive core isdescribed. The total quantity of explosive in the dual core varies alongthe length of the cord and the product is useful in metal expansionoperations.

5 Claims, 5 Drawing Figures PATENT EDUBI 17 I972 SHEET 1 [IF 2 INVENTORDavid Martin WELSH PATENT AGENT MANUFACTURE OF DETONATING FUSE CORD Thisinvention relates to detonating cord and in particular, to themanufacture of a composite detonating cord having a dual explosive coreof controlled variations. Such a detonating cord has particular use in,for example, metal expansion applications.

As is known in the explosives art, detonating cords are normallyproduced in long or continuous lengths and comprise essentially asingle, uniform core of explosive encased in a protective wrapping orsheath. Originally, the protective sheath consisted of a soft metal suchas lead but these lead sheathed cords have now generally been supersededby those having sheaths consisting of water resistant tape or textilewrappings, synthetic plastics and the like. The amount of explosive perfoot of length in the core may vary from a small quantity of from 0.1 toabout grains as in low energy detonating cord (LEDC), to as much as 50grains or more. Typical explosives employed as core material are, forexample, pentaerythritoltetranitrate (PETN),cyclotrimethylenetrinitramine (RDX), nitromannite,

lead azide, trinitrotoluene (TNT), cyclotetramethylenetrinitramine(HMX), lead styphnate or tetryl and mixtures of these.

In the explosives industry detonating cords are manufactured by one orother of the dry or wet processes. In the dry process relatively coarse,particulate, dry explosive which comprises the core material of the cordis encased in a continuous column by means of a wrap of tape-likematerial and thereafter encircled by means of textile yarns of the like.The cord may thereafter be coated with a waterproofing surface layer ofpitch, thermoplastic or the like. The dry process is normally employedin the manufacture of detonating cords having a core load of 25 grainsor more of explosive per foot of length.

In the wet process, the core is formed from a thickened aqueous slurryof particulate explosive which is wrapped with a textile braid andcovered in much the same manner as that employed in the dry process.Generally the wet process is employed in the manufacture of detonatingcord having a core load of 4 grains or more of explosive per foot oflength.

It has heretofore been the object and concern of the explosives industryto manufacture detonating cords having an absolute minimum of core loadvariation throughout the cord length in order to ensure constantdetonation characteristics along the cord, in particular, uniformlateral energy output. It has now been found that in certainapplications such as metal expansion, it is desirable to provide adetonating cord having an alternating or pulsating lateral energy outputwith a sub stantially constant linear velocity of detonation.

Accordingly, it is an object of the present invention to provide amethod of manufacture of a detonating cord wherein the cord contains anexplosive core load, which core load comprises alternating areas ofgreater and lesser explosive energy.

It is an additional object of the invention to provide a noveldetonating cord comprising two explosive energy cores commonly encasedin a protective sheath in sideby-side relationship, one of said energycores having areas of greater and lesser explosive content.

Other objects of the invention will become obvious from a considerationof the following disclosure and claims.

The novel method of manufacture of the invention comprises continuouslyforming a first braided textile stocking and directing a stream ofslurried particulate explosive through an orifice in a continuous anduniform column into said textile stocking. A second braided textilestocking is formed and a stream of at least one slurried particulateexplosive is directed through an orifice in a manner such that thestocking contains alternating areas of greater and lesser explosiveenergy. The two braided explosive-containing stockings are then boundtogether in side-by-side relationship so as to form a composite cordunit having regular alternating sections of explosives of differentenergy output.

The me th od of the invention and the product thereof may be more fullyunderstood by reference to the accompanying drawings wherein:

FIG. 1 is a sectional view of one embodiment of a finished detonatingcord made by the method of this invention;

FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1;

FIG. 3 is an elevational diagrammatic view of a portion of the apparatussuitable for use in the method of the invention;

FIG. 4 is an elevational diagrammatic view, partly in section of aportion of an alternative apparatus suitable for use in the method ofthe invention; and

FIG. 5 is a flow diagram of the process steps of the method of theinvention.

Referring in detail to FIGS. 1 and 2, there is shown a detonating cord 1having two inner explosive core sections 2 and 3. Core section 2comprises a continuous column of explosives 4 encircled by braidedtextile stocking 5. Core section 3 comprises a continuous columncontaining alternating explosives sections 6 and inert or non-explosivematerial sections 7. Core section 3 is encircled by braided textilestocking 8 and the core sections 2 and 3 are bound together byencircling textile wrap 9. An outer covering 9A of, for example, aflexible thermoplastic material is shown covering the whole.

Referring to FIG. 3, there is shown pressurized storage containers 10and 11, container 10 containing a quantity of slurried, particulateexplosive, for example, PETN, and container 11 containing a quantity ofinert particulate material, for example, a thermoplastic, a waterinsoluble inorganic salt or a water insoluble organic salt. Leading fromcontainers l0 and 11 are delivery lines 12 and 13 respectively, whichlines terminate at air-operated valve 14. Air cylinder 15 is adapted tooperate valve 14. Valve 14 comprises an exit line 16 having an orifice17 to which the slurried explosive and slurried inert material may bedelivered from containers 10 and 11. Below orifice 17 is textilebraiding head 18 by which means a braided textile stocking is formed onorifice 17 and is continuously withdrawn from orifice 17 as it is formedwhile at the same time the slurried particulate explosive and inertmaterial are alternately forced out of the center of orifice 17. Belowbraiding head 18, the textile covered cord 3 is delivered to a dryingoperation (not shown) preparatory to inspection and wrapping inside-by-side relationship with a second continuous explosive core cord 2which second cord is made by well known standard wet process methods.After wrapping, the two cords have applied thereto an outer protectivesheath or coating. Air lines 19 and 20 enter containers l and 11respectively and pressurized air (from sources not shown) is directedinto each of these containers. The pressure of the air in container may,if desired, be different from the pressure of that of the air incontainer 11.

Referring to FIG. 4, there is shown an apparatus similar to that shownin FIG. 3 except that the valve 14 and air cylinder of FIG. 3 arereplaced by excentric cam 21 which is rotated by drive means (not shown)to activate pinch valves 22 and 23 which alternatively close off theflow of slurry through lines 12 and 13 respectively.

Referring to FIG. 5, there is shown in sequential steps the variousoperations employed in the method of the present invention.

In one operation of the method of the invention employing the apparatusas shown in FIG. 3, a supply of typical detonating cord explosive, forexample, PETN in suitable particulate form is prepared as an aqueousslurry by combining the PETN grains with a quantity of water and asuitable thickening agent such as, for example, hydroxy ethyl cellulose.A quantity of the PETN/water slurry is placed in container 10. Aquantity of non-explosive or inert slurry material of similarconsistency is placed in container II and air pressure is applied to thesurface of the slurry in each container through air lines 19 and 20. Thepressure of the applied air is adjusted to provide the desired rate ofslurry flow. Air cylinder 15 operates valve 14 in timed reciprocatingmotion by well known means (not shown) to allow delivery of theexplosive slurry and the inert material slurry in alternating sequencefrom containers l0 and 11 and delivery lines 12 and 13 to exit line 16and orifice 17. As the slurries are successively forced from orifice 17and into the braided stocking, a cohesive, string-like configuration isassumed having along its length regularly alternating explosive andnon-explosive sections. The textile sheathed cord is then passed to adrying operation (not shown) and, thereafter inspected. The alternatingsection cord is then wrapped by means of a textile braid in side-by-siderelationship with a second continuous explosive cord and an outercovering of, for example, thermoplastic material is applied. The thuscompleted two-core composite detonating cord may then be wound on atake-up spool for storage or shipment.

In the operation of the method of the invention employing the apparatusas shown in FIG. 4, all the steps described heretofore with respect tothe apparatus of FIG. 3 are the same with the exception of the meansemployed to achieve an alternating or pulsating extrusion of the slurry.

Referring to FIG. 4, it can be seen that when excentric cam 21 isrotated by a drive means (not shown) the flow of slurry through lines 12and 13 is interrupted in a sequential manner by pinch valves 22 and 23thus permitting the extrusion of the slurry at orifice 17 in a column ofalternating explosive and non-explosive sectrons.

In the operation of the method employing either the apparatus of FIG. 3or FIG. 4 and using a PETN explosive of grain size normally used for themanufacture of detonating cords of 4 grains or more of explosive perfoot of length containing a small percentage of water and thickener, ithas been found that air pressure of about 10 p.s.i. on container 10produces a detonating cord core section containing an average explosiveload of 24 grains per foot of length when the orifice 17 has an internalcross section of 0.166 inch. An air pressure of about 40 p.s.i. producesan average core load of 52 grains of explosive per foot of lengththrough the same orifice. With an inert material such as, for example,powdered polypropylene resin having a slurry consistency and grains sizesimilar to that of the PETN, slurry similar core loads of inert materialare provided.

The composite cord comprising the bound-together continuous andnon-continuous core cords provide a finished detonating cord havingsections of greaterand lesser quantity of explosive which sections maybe any length as desired since the section length is a function of thelength of time each slurry is permitted to flow from the alternativesources of supply. It will be obvious that the quantity of explosives ineach of the greater and lesser energy sections of the compositedetonating cord can be varied depending on the thickeness or density ofthe explosive and the inert slurries and on pressure of the airdelivered to each of the storage container. Too thin a slurry willgenerally result in an unsatisfactory product.

It will be appreciated that, if desired, in the production ofalternating core cord 3 using either the apparatus of FIG. 3 or FIG. 4,one of container 10 or 11 containing inert slurry material may be leftempty and the air supply to the empty container may or may not be cutoff. As a consequence of such procedure, the resultant cord 3 willcomprise void areas or sections within the braided stocking 8 in placeof sections containing inert slurry material. Several advantages may begained through the use of such procedure. Labor and material involved inmaking the inert slurry is eliminated and additionally the sections ofgreater energy in the final composite cord may be more readilyidentified by a bumpy cord appearance.

It will be obvious from the foregoing description that a compositedetonating cord comprising alternating sections of greater and lesserexplosive energy may also be produced through the use of, for example,explosives having different energy values or strengths in themanufacture of the irregular or alternating core cord 3 of FIG. 1 andFIG. 2. That is to say, continuous column core may comprise, forexample, PETN explosive while the alternating core may comprise TNT asthe explosive ingredient. It will also be obvious that a combination ofquantities and kinds of explosives may be used in the alternating corecord. For example, one section may comprise a core load of, say, 50grains per foot of PETN and the adjacent section may comprise a dilutedexplosive content, say 10 grains per foot of PETN or TNT instead of acompletely inert non-explosive material. The production of such cordsusing the apparatus shown in the figures of the drawing may be readilyaccomplished by placing a selected slurry of PETN in container 10 and aselected slurry of adulterated PETN or TNT in container 11. Applicationof appropriate air pressure to each container will provide extrudedsections through orifice 17 of explosive of alternating explosiveenergy. Similarly the explosive adapted for use in the continuous corecord 2 of FIGS. 1 and 2 may comprise a useful particulate explosive suchas PETN mixed with an inert adulterant in order to further reduce theactual quantity of explosive present and hence also reduce the actualexplosive energy upon detonation of the portion of the composite cord.

It will be appreciated that a wide variety of slurriable particulateexplosives and mixtures thereof may be utilized for the processdescribed.

What we claim is:

l. A method of producing a dual core detonating fuse cord having alongits length regular alternating sections of different potential energyoutputs comprising the steps of:

a. continuously forming a first braided textile stocking;

b. ejecting a stream comprised of regularly alternating portions ofslurried particulate explosive and slurried particulate inertnon-explosive through an orifice in a continuous column into said firsttextile stocking;

c. drying the filled, first braided, textile stocking;

d. continuously forming a second braided textile stocking;

e. ejecting a stream of slurried particulate explosive through anorifice into a continuous column into said second textile stocking;

f. drying the filled, second braided, textile stocking;

g. wrapping together in side-by-side, linear relationship said filled,first and second textile stockings to form a dual cord; and

h. covering the wrapped dual cord with a protective sheath.

2. A method as claimed in claim 1 where a void is substituted for theslurried particulate non-explosive in the said first textile stocking.

3. A method as claimed in claim 1 wherein the streams of slurriedexplosive and non-explosive are ejected by pneumatic force.

4. A method as claimed in claim 1 wherein the particulate explosive isselected from the group consisting of pentaerythritoltetranitrate,cyclotrimethylenetrinitramine, nitromannite, lead azide,trinitro-toluene, cyclotetramethylenetetranitramine,lead styphnate,tetryl and mixtures of these.

5. A method as claimed in claim 1 wherein the particulate inertnon-explosive is selected from the group of particulate thermoplastics,water-insoluble inorganic salts and water-insoluble organic salts.

1. A method of producing a dual core detonating fuse cord having alongits length regular alternating sections of different potential energyoutputs comprising the steps of: a. continuously forming a first braidedtextile stocking; b. ejecting a stream comprised of regularlyalternating portions of slurried particulate explosive and slurriedparticulate inert non-explosive through an orifice in a continuouscolumn into said first textile stocking; c. drying the filled, firstbraided, textile stocking; d. continuously forming a second braidedtextile stocking; e. ejecting a stream of slurried particulate explosivethrough an orifice into a continuous column into said second textilestocking; f. drying the filled, second braided, textile stocking; g.wrapping together in side-by-side, linear relationship said filled,first and second textile stockings to form a dual cord; and h. coveringthe wrapped dual cord with a protective sheath.
 2. A method as claimedin claim 1 where a void is substituted for the slurried particulatenon-explosive in the said first textile stocking.
 3. A meThod as claimedin claim 1 wherein the streams of slurried explosive and non-explosiveare ejected by pneumatic force.
 4. A method as claimed in claim 1wherein the particulate explosive is selected from the group consistingof pentaerythritoltetranitrate, cyclotrimethylenetrinitramine,nitromannite, lead azide, trinitrotoluene, cyclotrhylenetetranitramine,lead styphnate, tetryl and mixtures of these.
 5. A method as claimed inclaim 1 wherein the particulate inert non-explosive is selected from thegroup of particulate thermoplastics, water-insoluble inorganic salts andwater-insoluble organic salts.